The present invention relates to a biofeedback system which is used for indicating the state of mental activity of a human subject.
It is well known that human mental activity can be measured in terms of (1) electrical activity of the brain as represented by the brain waves, (2) electrical potential changes measured by electromyographic method, (3) potential changes at the surface of the skin or (4) temperature at the skin surface. It is also known that these physiological phenomena can be used to control the autonomic nerve system of the human subject or used as a means for rehabilitation. More specifically, when a human subject is in a relaxed state of mind, the predominant brain waves are the so-called alpha waves and the muscle potential falls to a low level, while there are increases in the electrical resistance and temperature of the skin. Conversely, when the subject is in a nervous, strained or highly excited state, the beta waves are predominant, the muscle potential becomes high and there are decreases in the electrical resistance as well as temperature of the skin.
Thus, an indication of such physiological signals can serve as a guide to lead the human subject into a relaxed state of mind. This kind of mind control is called "biofeedback" and apparatus used for such purposes is part of a biofeedback system.
However, because the presence of a single physiological signal is not necessarily a true indication of relaxation it is desired that there be as many sources of physiological clues as possible. One approach to this problem seemingly is to combine a plurality of specific measurement devices in a single unit for simultaneous indication of the measured data. This approach however requires the user constantly to scan his eyes over the displayed data. Because of this factor the use of plural measurement devices appears to be unsatisfactory as a guide for mind control purposes.